1) Field of the Invention
The present invention relates to a method of preparing calcium carbonate using a direct carbonation reaction.
2) Background of Related Art
Recently, as power consumption is significantly increased every year with the industry development and the improvement in the quality of life, a greater amount of fossil fuel has been consumed. Accordingly, an emission amount of sulfur dioxide gas has been increased. Therefore, a flue-gas desulfurization system to remove sulfur dioxide gas has been continuously increased, so that an amount of flue-gas desulfurization gypsum to be treated is gradually increased. In order to utilize the flue gas desulfurization gypsum, ammonium sulfate fertilizer has been produced. Simultaneously, calcium carbonate, which is a byproduct of the ammonium sulfate fertilizer, has been produced. The calcium carbonate may be commercially utilized according to the purity and the forms thereof. According to the related art, in order to treat the flue gas desulfurization gypsum, two consecutive reaction steps are performed as expressed in chemical formula 1.CO2(g)+2NH4OH→(NH4)2CO3(aq)CaSO4.2H2O+(NH4)2CO3(aq)→CaCO3(s)+(NH4)2SO4+2H2O  [Chemical formula 1]
The ammonium sulfate having high product yield and high purity can be produced through the reaction. The purity of the ammonium sulfate is increased since most residues of the flue gas desulfurization gypsum remain in the form of solid residues. In addition, if impurities remain in the ammonium sulfate, the impurities may be simply filtrated from the ammonium sulfate. When taking into consideration the solubility of the ammonium sulfate and the calcium carbonate, the ammonium sulfate remains in a solution since the ammonium sulfate has high solubility, and most parts of the calcium carbonate is precipitated without being dissolved. Accordingly, the crystal of the ammonium sulfate having the high purity can be obtained after the insoluble impurities has been removed through a filtering process and the precipitation has been performed. Meanwhile, since the calcium carbonate has low solubility, calcium carbonate having high purity may not be obtained through the above method.
As the related art, there is provided “sequestration of carbon dioxide by the waste gypsum” disclosed in Korean Unexamined Patent Publication No. 10-2010-0008342 (published on Jan. 25, 2010).